This invention relates to portable fluid evacuators which are disposable and self-contained.
The practice of drawing a vacuum on a catheter placed in a patient's body to remove fluid buildup following surgery is a common medical technique. It has been found that removal of fluids from a wound will accelerate healing and reduce the risk of infection. Fluid evacuation has been typically accomplished by means of a central suction system or by power driven vacuum pumps. This has proven unsatisfactory because it is difficult or impossible to move the patient without first disconnecting him from vacuum supply. Further, the negative pressure supplied by such vacuum units is difficult to maintain at a constant value. Moreover, the use of power driven electric pumps is potentially hazardous since the fluid pathway through the wound drain catheter creates an electrical connection between the pump and the patient which exposes the patient to risk of shock or electrocution.
The prior art attempted to overcome these problems by providing portable, self-contained, non-electrical fluid evacuators. These evacuators typically comprise collapsible reservoirs biased with springs or weights which bias them to open after being manually compressed. Since these devices are self-contained and portable, the patient may be easily moved without disconnecting him from the device. However, many of these prior art devices are not capable of maintaining a substantially constant vacuum over their entire filling range. Constant vacuum pressure is desirable, since this permits uniform removal of fluid from the patient. If the vacuum is too high, lesions may be caused by sucking delicate tissue into or against the drainage tube. Conversely, if the vacuum is too low, fluid will accumulate and the device will be ineffective. Thus, a substantially constant pressure fluid evacuator is considered highly advantageous.
A further problem with prior art evacuators is that many of them are not pre-evacuated by the manufacturers, but rather, must be manually evacuated just prior to use. Typically, a nurse or medical assistant will apply force with one hand to manually compress and collapse the reservoir, and, with the other hand, insert a catheter or plug into the device before removing such compression force. Evacuation at the point of use is, therefore, awkward and time consuming.
An additional disadvantage of fluid evacuation devices which are evacuated at their point of use is that they are shipped in an unevacuated state. Thus, they require more storage space than the pre-evacuated devices. Obviously, this increases shipping, storage, and sterilization costs. Further, it is difficult, if not impossible, to completely evacuate a fluid reservoir at its point of use. Thus, when the reservoir is initially connected to draw fluid from the patient, it may still contain a substantial quantity of air. Since the space devoted to containing such air is wasted, the effective capacity of the reservoir is decreased. Therefore, the reservoir size must be larger than would otherwise be necessary. This increases manufacturing costs and further increases the costs of sterilization, shipment, and storage.
One reference, Abramson U.S. Pat. No. 4,161,179, suggests pre-evacuating a fluid evacuation device. The Abramson device comprises a flexible reservoir biased with leaf springs. Abramson teaches that after the reservoir has been pre-evacuated, the catheter is clamped to maintain the vacuum created by such pre-evacuation. Subsequently, after the catheter has been placed in the wound, the clamp is removed to permit the device to draw fluid. However, this method of maintaining a vacuum is obviously disadvantageous, since the clamp may be accidentally dislodged either during shipment or be a nurse while handling the device. Moreover, such a clamp, in order to maintain the vacuum, would have to exert considerable force on the catheter tube. Thus, if the device were stored for a long period of time, the resiliency of the catheter tube may not be sufficient to permit it to return to its normal shape, and the tube may remain permanently crimped. Therefore, the flow of fluid from the wound to the evacuator would be substantially restricted.